Crude drugs are used as an active ingredient for cold and stomach medicines, nourishing tonics and the like. Many oral liquid preparations containing crude drug extracts are sold for practical use. A dosage of these commercially available liquid preparations containing crude drug extracts are usually 25 to 100 mL. However, considering the compliance of the consumers, who are old persons, children and persons having a weaker physical strength due to diseases, a dosage of medicines should preferably be reduced as much as possible. In order to administer a minimum dose, and furthermore to be effective even in a reduced dosage, crude drug extracts have to be contained in the whole amount of a liquid preparation in a high concentration. In this case, as a concentration of the crude drug components increases, contact between the crude drug components increases to cause aggregation, resulting in the problem that a generating amount of precipitation and turbidity increase with the course of time.
pH of a liquid preparation containing crude drug extracts has to be set up as low as possible to maintain the taste and the preservation. On the other hand, it is known that precipitation and turbidity are generated with the course of time by reducing the pH, and it has resulted in bringing about the problems that an unpleasant feeling is given to the consumers and the product value is damaged and that an influence to the effectiveness is concerned about.
In these liquid preparations containing crude drug extracts, generally it is well known that surfactants used as a solubilizer suppress the generation of precipitation and turbidity with the course of time. In this method, however, there have been the problems that a large amount of surfactants is required and therefore an influence exerted to organisms by the surfactants is concerned about and that the surfactants are susceptible to hydrolysis at a lower pH and therefore the solubilizing effect is reduced.
A method for preventing precipitation and turbidity originating in a crude drug by adding a polyoxyethylene-hardened castor oil derivative and polyvinylpyrrolidone at pH 3.0 to 4.5 is reported in Japanese Patent Application Laid-Open No. 61-268267, and a liquid preparation containing crude drug extracts which is adjusted to have a pH of 2.2 to 3.8 by adding polyoxyethylene-polyoxypropylene glycol and which is stable over a long period of time is reported in Japanese Patent Application Laid-Open No. 2000-38345. However, these methods are not sufficient, and it is difficult to apply them to liquid preparations containing crude drug extracts in a high concentration.
Accordingly, an object of the present invention is to provide a stable liquid preparation containing crude drug extracts which is suppressed in generating precipitate and suspended contents with the course of time even if crude drug extracts are contained in a high concentration.